1. Field of the Invention
The present invention relates to a signal lamp for vehicles, the reflective surface of which is composed of a plurality of reflecting elements. More particularly, the present invention relates to a structure of a reflective surface which improves in external appearance.
2. Related Art
As shown in FIGS. 12 to 14, a conventional signal lamp for vehicles is generally provided with a light source bulb 2, a reflector 4 having a reflective surface 4a for reflecting light forward sent from the light source bulb 2 and a lens 6 arranged in the front of the reflector 4.
Recently, many of signal lamps for vehicle are composed as follows. As shown in each drawing, the reflective surface 4a is composed of a plurality of diffusing reflection elements 4s, so that the burden imposed on the light diffusing function of lens steps 6s formed on the inner surface of the lens 6 can be reduced. Due to the foregoing, it becomes possible to ensure a feeling of transparency and depth of the lighting device.
However, the following problems may be encountered in the conventional signal lamp for vehicles described above. When the lighting device is viewed from the front side under the condition that the light source bulb 2 is turned on, brightness of the reflecting light, which has been reflected in a portion on the reflective surface 4a, greatly changes depending upon the portion. Due to the foregoing, the lighting device looks unattractive when viewed from the outside.
The above problem will be explained in detail as follows. For example, as shown in FIGS. 13 and 14, when each diffusing reflection element 4s has a light diffusing function in the transverse direction, and on the other hand when it has no light diffusing function in the vertical direction, only light reflected in the central region of the light diffusing reflection element 4s in the transverse direction is sent to the direction of the optical axis Ax of the reflector. Therefore, when the lighting device is observed from the front side under the condition that the light source bulb 2 is turned on, the rectangular central region 4s1 of each light diffusing reflection element 4s in the transverse direction, that is, the optical axis direction reflecting region is seen as a belt-shaped bright portion B, the brightness of which is high as shown in FIG. 15. However, luminance of this bright portion B is different from each other according to the position at which the diffusing reflection element 4s is arranged as shown by the mesh in the drawing.
That is, in the light diffusing reflection element 4s distant from the filament 2a (light source) of the light source bulb 2, illuminance of the incident light emitting from the filament 2a becomes low. Therefore, luminance of the bright portion B of the light diffusing reflection element 4s also becomes low. In the case of a linear light source such as the filament 2a described above, the light distribution characteristics (spatial distribution of luminous intensity) are described as follows as shown in FIGS. 16(a) and 16(b). Luminous intensity in a direction close to the central axis Axf of the filament 2a is lower than luminous intensity in a direction perpendicular to the central axis Axf.
Therefore, in the case where the filament 2a extends in the perpendicular direction as shown in FIG. 15, even if the distance from the filament 2a is the same, illuminance of the diffusing reflection element 4s located in the upper or lower position of the optical axis Ax is lower than illuminance of the diffusing reflection element 4s located on the side of the optical axis Ax when light emitting from the filament 2a is incident. For the above reasons, when the entire reflective surface 4a is observed, a portion close to the side of the optical axis Ax is very bright, however, a peripheral portion is very dark, that is, brightness of the entire reflective surface 4a is not uniform. Due to the foregoing, the lighting device looks unattractive.